Normal liquid crystal display devices have a relatively simple structure. They are formed essentially by two separated substrates, at least one of which is transparent, a liquid crystal compound enclosed between the substrates and conducting electrodes arranged on opposing faces of the substrate which face each other and which are arranged in such a way as to represent different displaying symbols. A voltage source is arranged so as to apply a field between the electrodes in the space formed between the substrates. The applied field acts upon the liquid crystal compound to change its transmission or reflection characteristics.
These liquid crystal display devices are used in numerous applications and in particular in pocket calculators, wrist-watches, measuring instruments, pagers and several other electronic instruments. The advantage of such display devices resides in the fact that they can be controlled directly by microplates for integrated circuits and that they can display several symbols in a reduced space.
FIGS. 1 and 2 are plane views respectively on the front face of a first substrate 1 and the back face of second substrate 2 of a liquid crystal display device of a known kind. The two substrates or plates 1 and 2 are both provided with a set of electrodes. The electrodes on each plate are subdivided into those forming fixed display symbols and those which are grouped together to form seven segments in a shape of an "8".
Because there are many electrodes, only some of these electrodes on the two plates have been designated by references. Thus, the electrodes on the plates 1 and 2 forming fixed symbols, such as the words "OFF", "ON" and "AUTO", are respectively designated by the references 1.1, and 2.1, while the electrodes forming the groups of seven segments are designated by the references 1.2 and 2.2.
All the electrodes are arranged on the inside of a sealed frame 3 which forms with the two plates 1 and 2 a cell on the inside of which is enclosed a liquid crystal film 4. Connection terminals 1.3 are arranged on the front plate 1, outside of frame 3. Conductive tracks 1.4 connect these terminals to the electrodes 1.1 and 1.2. Certain terminals 1.3, designated by the references 1.31, 1.32 and 1.33, are connected to the electrodes on plate 2 by the means of connection bridges (non represented A, B and C) which connect the two substrates to each other at the level of the frame 3.
The electrodes of plate 2 are subdivided into three parts, to which are respectively connected the three terminals 1.31, 1.32 and 1.33. The first part 5 reunites all the electrodes 2.1 forming the fixed symbols and all the electrodes 2.2 forming a first segment of the seven segment in the shape of an "8". The second part 6 reunites all the electrodes 2.2 forming the second, third and fourth segments of the seven segments in the shape of a "8". The third part 7 reunites all the electrodes 2.2 forming the fifth, sixth and seventh segments of the seven segments in the shape of an "8". The parts 5, 6 and 7 are respectively connected to terminals 1.33, 1.31 and 1.32.
To display a fixed symbol, for example the word "ON", a voltage is applied between electrode 7 and a terminal 1.34, which is connected indirectly to electrodes 1.1 having form of the word "ON". The resulting field created by the superposed parts of electrodes 1.1 forming the word "ON" and the electrode 7 change the optical characteristics of the liquid crystal display device, so as to display this word.
To display a changeable symbol by way of electrodes 2.2 forming the groups of seven segments in the shape of an "8", for example to display a "3" at the position on the plate 1 designated by the reference 8, a voltage is applied between terminals 1.35 and 1.36 and the terminals 1.31, 1.32 and 1.33. As in the above case, the resulting field between the superposed parts of the electrodes 1.2 forming the group of seven segments at the extreme left of plate 1 (as can be seen on FIG. 1) and the electrodes 5, 6 and 7, change the optical characteristics of the liquid crystal display device so as to display the number "3" at position 8.
Although the device described hereabove is capable of displaying at the same time fixed symbols and changeable symbols, a need currently exists for more flexibility in the kind of the information which can be displayed by the part capable of displaying changeable symbols. By using groups of symbols of seven segments in the shape of an "8", the kind of information which can be displayed by this part is limited to simple alphanumerical representations that is the numbers "0" to "9", the symbol "-" and the letters of the alphabet. Furthermore, a certain confusion is possible between several characteristics, for example between "B" and an "8", or between "2" and a "Z".
The patent U.S. Pat. No. 4,522,691 describes a display device having several display electrodes formed in parallel on the surface of a first substrate and several counter-electrodes formed in parallel on the surface of a second substrate spaced apart from the first substrate. The display electrodes and the counter electrodes are orientated so that their directions cross each other at a straight angle, thus forming a matrice of displaying elements of which each element may be selected by applying selectively a switching voltage between one of the display electrodes and one of the counter electrodes. This device constitutes a matrix display which can display changeable symbols according to a known multiplexing system, thus offering a great flexibility for the kind of symbols which may be displayed, than the one which may be realized with a display using seven segments.
However the display device described in this document cannot be obtained by adapting the construction used for the display device illustrated in FIGS. 1 and 2 as described hereabove. When considering FIG. 3 of the patent U.S. Pat. No. 4,522,691, it can be seen that both the display electrodes and the counter electrodes cross the entire surface of the substrate on which they have been respectively formed in such a way that they are occupying this entire surface.